Many pearlescent or nacreous pigments are based on micaceous or other lamellar substrates which have been coated with a metal oxide layer. As a result of reflection and refraction of light, these pigments exhibit pearl-like luster and depending on the thickness of the metal oxide layer, they can also exhibit interference color effects. A good description of this type of pigment can be found in U.S. Pat. Nos. 3,087,828 and 3,087,829.
The pearlescent pigments encountered most often on a commercial basis are titanium dioxide coated mica and iron oxide coated mica pearlescent pigments. Both types are well known in the art. It is also well known that the metal oxide layer may frequently be overcoated.
In U.S. Pat. No. 3,087,828, there is a description of depositing an Fe.sub.2 O.sub.3 layer onto a TiO.sub.2 layer. In U.S. Pat. No. 3,711,308, a pigment is described in which there is a mixed layer of titanium and iron oxides on the mica and that is overcoated with titanium dioxide and/or zirconium dioxide. U.S. Pat. No. 3,874,890 describes pigments coated with TiO.sub.2 or ZrO.sub.2 being overcoated with iron (II) hydroxide which is thereafter oxidized to Fe.sub.2 O.sub.3. U.S. Pat. No. 4,146,403 describes an iron oxide-coated mica pigment with a very thin layer of TiO.sub.2 or Al.sub.2 O.sub.3 and U.S. Pat. No. 4,086,100 describes rutile TiO.sub.2 -coated mica with an additional top layer composed of coloring metal oxides including, inter alia, Fe.sub.2 O.sub.3.
It has now been discovered that when an iron oxide-coated mica pigment is overcoated with a colorless metal oxide having a refractive index of at least about 2.0, an intense coloring effect is achieved when the coating amount falls within certain ranges. If the metal oxide has a lower refractive index or if it has the correct refractive index but is present in an incorrect amount or if the layers are inverted, the intense coloring effect is not realized.
It is accordingly the object of this invention to provide new intensely colored pearlescent pigments. This and other objects of the invention will become apparent to those skilled in this art from the following detailed description.